Synchronous ac rectified flyback converter utilizing boost inductor

Abstract

A flyback converter utilizes a boost inductor coupled between a source of AC power and a synchronous rectifier to provide power factor correction. The synchronous rectifier includes four field-effect transistors configured in a bridge arrangement. Control circuitry controls the on / off states of opposite pairs of the FETs to provide synchronous rectification of the AC power. A primary winding of the flyback transformer is coupled in series with a storage capacitor across the output of the synchronous rectifier. A circuit, which includes a switching transistor, is also coupled across the output of the synchronous rectifier to provide a low resistance path when the switch is closed. The cores of the boost inductor and the transformer are loaded with energy when the switch is closed. When the switch opens, the energy stored in the magnetic cores is transferred to the output via the transformer secondary winding and rectification circuitry. In one embodiment, a separate switching transistor is not used and its function is performed by the rectifier FETs.

Description

RELATED APPLICATION[0001]This application is in the same technical field as U.S. patent application Ser. No. 12 / 646,152, filed Dec. 23, 2009, the disclosure of which is incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to power supplies, also known as power adapters and power converters. In particular, the invention concerns a flyback converter which utilizes a boost inductor coupled between a source of AC power and a synchronous rectifier to provide power factor correction and low conduction loss associated with rectification.BACKGROUND OF THE INVENTION[0003]Power factor is the ratio of real power to apparent power. Real power is the average (over a cycle) of the instantaneous product of current and voltage. Apparent power is the product of the RMS value of current times the RMS value of voltage. Real power is the power required to do the needed work. Apparent power is the power that is supplied by the electricity generator (e.g., a power co...

AI Technical Summary

Problems solved by technology

Most power supplies, however, present a non-linear, rather than a linear, load impedance to the AC mains.

High harmonic content in the current waveform not only lowers the power factor, the harmonics may travel down the neutral line of the AC mains and disrupt other devices connected thereto.

However, due to component size constraints, power factor correction circuits which use active circuits are more common.

Such an arrangement increases component count and associated cost.

Use of a diode bridge rectifier causes conduction loss.

This results in continuous conduction losses which decrease the efficiency of the power converter.

The conduction losses also cause the undesirable generation of heat.

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